1. Field of the Invention
The present invention relates to lighting engineering, particularly to a filter changer for theater light units.
2. Description of Prior Art
Known in the art (USSR Author's Certificate No. 735,860 to me and two others, 1980) is a universal filter changer for mounting on theater light units. This filter changer comprises a casing, means for attachment of the casing to a light unit, a set of filter frames, and a mechanism for switching the filter frames between two extreme positions. The switching mechanism consists of a stationary part, fixed to the casing, and a movable part, which can rotate with respect to the stationary part together with filter frames which carry corresponding color filters. The movable part is driven by an electromagnet.
This filter changer, however, entails a number of disadvantages; the main ones are as follows:
(a) the method of fixation of the light filters in their extreme positions is unreliable and hence may result in failure;
(b) the clamp for attachment of the filter changer to the lighting unit makes it difficult to align the center of light filters with the optical axis of the lighting unit; this offcenter alignment causes edge illumination;
(c) the light filter frames supplied with the filter changer cannot be used for mounting thin-film filters; this restricts the dimensions of the light filters used in the device, i.e., it precludes the use of large-diameter filter frames because of their heavy weight.